This invention relates to microwave filters and, in particular, to waveguide filters employing dielectric resonators.
Conventional mounting arrangements for dielectric resonators involve extensive modification of the waveguide. Typically, an aperture or iris is made in the wall of the waveguide into which extends a portion of the dielectric resonator. The bulk of the resonator is shielded by a metallic housing mounted on the exterior side of the waveguide wall. The length of the filter which corresponds to the direction of propagation of the electromagnetic energy in the waveguide can be shortened by using plural filters at common cross-sectional planes of the waveguide to make the filter assembly more compact. Each time an additional dielectric resonator filter is used, however, there is a cost increment in manufacturing the filter since each resonator requires a separate metallic housing and additional modifications must be made in the waveguide.
In a variety of applications, particularly in the case of existing radio systems, it would be extremely desirable to be able to modify the electrical characteristics of the equipment with minimal physical changes in the actual equipment. Due to the precise machining required at microwave frequencies, physical modifications are expensive. Furthermore, the physical design of existing equipment may place severe space constraints on the modifications which are possible. Accordingly, a filter structure which can be inserted within an existing waveguide which is economical and provides suitable electrical characteristics is useful in numerous applications without equipment modification beyond the mere disassembly and reassembly necessary to install the filter for operation. Of course, the latter operations may also be avoided in the case of new equipment.